Crystal structure of Thermotoga maritima α-glucosidase AglA defines a new clan of NAD+-dependent glycosidases

Jacinta A. Lodge, Timm Maier, Wolfgang Liebl, Volker Hoffmann, Norbert Sträter

Research output: Contribution to journalArticlepeer-review

59 Scopus citations


Glycoside hydrolase family 4 represents an unusual group of glucosidases with a requirement for NAD+, divalent metal cations, and reducing conditions. The family is also unique in its inclusion of both α- and β-specific enzymes. The α-glucosidase A, AglA, from Thermotoga maritima is a typical glycoside hydrolase family 4 enzyme, requiring NAD+ and Mn2+ as well as strongly reducing conditions for activity. Here we present the crystal structure of the protein complexed with NAD+ and maltose, refined at a resolution of 1.9 Å. The NAD+ is bound to a typical Rossman fold NAD+-binding site, and the nicotinamide moiety is localized close to the maltose substrate. Within the active site the conserved Cys-174 and surrounding histidines are positioned to play a role in the hydrolysis reaction. The electron density maps indicate that Cys-174 is oxidized to a sulfinic acid. Most likely, the strongly reducing conditions are necessary to reduce the oxidized cysteine side chain. Notably, the canonical set of catalytic acidic residues common to other glucosidases is not present in the active site. This, combined with a high structural homology to NAD-dependent dehydrogenases, suggests an unusual and possibly unique mechanism of action for a glycoside-hydrolyzing enzyme.

Original languageEnglish
Pages (from-to)19151-19158
Number of pages8
JournalJournal of Biological Chemistry
Issue number21
StatePublished - 23 May 2003
Externally publishedYes


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